Signaling system



May 31, 1932. R. s. BAILEY ET AL SIGNALING SYSTEM Filed Oct.

11. 1930 8 Sheets-Sheet 1 R. 5. BA ILEY uwz/vrops: N. 0. NE WBY D. L.MOOD V A TTORNE Y May- 31, 1932;

R. S. BAILEY ET AL SIGNALING SYSTEM Filed Oct. 11, 1930 OPERATORS 722 EPHONE' CIRCUIT 8 Sheets-Sheet 2 R. 5. BA ILE V INVENTORSI N. 0. NE W8) 0. L .MOODV FIG. 4

May 31, 1932. ms. BAIL EY ET AL 1,360,446

SIGNALING SYSTEM Eiled Oct. 11,,1930 8 Sheets-Sheet 4 INVENTORS: MDNEWBV DLMOODV (7 ATTORNEY May 31, 1932. R. s. BAILEY ET AL omBo! 2 NR R. 5. BAIL E) INVENTORS N. 0. NEWS) By QLMOODV ATTORNEY May 31, 1932.

R. s. BAILEY ET AL.

SIGNALING SYSTEM 8 Sheets-Sheet 6 Filed Oct. 11, 1930 R. 5. BAIL [V INVENTORS: N. 0. NWBV DLMOODV ATTORNEY May 31, 1932.

.SOONTONE R. s. BAILEYET AL 1,360,445

SIGNALING SYSTEM Filed Oct. 11, 1950 8 Sheets-Sheet 7 6 A TTORNFY y 1932- R. s. BAILEY ET AL 1,860,445

SIGNALING SYSTEM Filed Oct. 11, 1950 8 Sheets-Sheet 8 29 "OPERA TORS TELEPHONE '19 OPERA 70/? FIG. 8

POLAR/2E D R. S. BAILEY m/mvrms N. DNEWBY D. L M000) Patented May 31, 1932 UNITED STATES PATENT; ore-ice RAND, snninnr, or MONTGLAIB, AND

AND n-wien'r L. MOODY, or nnniesrnan,

NEAL n. NEWBY, or woonnlnon, new JERSEY,

new YORK, ASSIGNOBS To AMERICAN rnnnrnona Ann sameness GOMPANY, A conronarron on NEW YORK SIGNI'ALIVNG sYsTnM Aliplication filedOctober 11,1930. Serial No. 488,110.

I This invention relates to signalingsysteins and more particularly to what are known as two-way straightforwardsystems employing V alternating currents," within the voice frequency range, foroperating both the calling and supervisory .signa-l apparatus at both ends of the line. i

In many cases involving long toll lines the signaling conditionsIvary considerably wit the character of the circuits and apparatus associated with the line :such, for example, as

the delay circuits used tions p time interval to hold the signal current on.

inv conjunction with echo suppressors, etc. Under such condi- 't is difiicult to determine the proper the line to insure satisfactory operation of the receiving circuit at the distant 'enddue to the fact that the sameline' may present 'diflierentsignalingconditions at varioustimes on account of changes in the associated apparatus, changing weatherconditions, etc, which otherwise would have no detrimental effect on theitransmissioncharacteristics or I ee cont,

operation of the line. 7 I r The object of the invention therefore is to conserve the signaling" time of lines of this character while at the same timeinsuring positive'operation of the desired signal apparatusbeforeth'e signal current impulse is terminated.

A feature of the invention, whereby the. foregoing obgect is attained, I'GSlClGS inan ar-- rangeinent for transmitting current etapredoternziinedv frequency from the inward end back over the line to the calling endas soon as an incoming signal arrives. This current i hich may he termed a cutofi impulse is received at the outward or calling end of the line and immediately cuts of? the signaling current. EThe cutoii impulse is in turn out of? when the signal 'current-- ceases to flow. When the original signal current ceases to flow the line lamp at thereceiving station is lighted, r I e The invention will" be understood from the following nescr'iption ,oiithe initiation and completion 'ofa call over a toll line arranged in accordance therewithand from the accmpanvinq'drawing's', Figs; 1, 2, 3 representing a not the circuit arrangement at one end oithe toll line and Figs. 4,5, 6v and 7 representing a duplicate arrangement at the other end includinganoperat ors telephone circuit, while Fig. 8represents a switching trunk extending from an inward toll operators position to a suhscribers B operators position and thence to a called subscriber. Fig.7 9

represents thearrangement of Figs. 1 to .8 of the drawing. y

' In the following description the reference characters used ,ha-ve,1 for convenience been chosen in groups-of100,those from 101 to 1 99 referring ,to Fig. 1,201 to 299 to Fig. 2, etc;-

' rupted at acycle rate, to the line as .a call or connect signal which operates relays-at the distant exchange to connect a 10.00/ c 'cle:answer-backsignal to the line. The connect; signal lights the guard or connect lamp at theinward operatofls position, connect-s theoperatofls telephone to the line and transinits'three- Zips of tone back to the originab ing operator as .a signal to pass the desired; destination of the call. 7 1

The 1000/30 cycle answer-back signal dis connects the 1400/20 connect signal which in turn disconnects the 1000 30answer-back signal.

The originating operator 'nowgpasses the designation of the wanted subscribers ext change, reached over the switching trunk T,

p and the inward operator plugs into the trunk.

This extinguishes the connect 1amp705, disg c connects the inward opera-torfrom} the line and connects the distant Bvoperator to; the

trunk inthe well known straightforward manner. The originating toll operator-"is now in direct conversational connection with i the distant B operator and passes the number of the desired subscriber after receiving the usual two zips of order tone.

When the B operator plugs into the subscribers' line relays 719 and 511 operate to transmit a 1000/20 signal back over the line which lights the cord supervisory lamp before the originating operator. The subscriberis also rung undercontrol of interrupter 726 and relays 724, 805, 806 and 807.

When the called subscriber answers the 1000/20 signal is disconnected which extinguishes the supervisory lamp before the originating operator.

When the called subscriber hangs up a 1000/20 signal is again applied to the line torelight the cord supervisory relay before the originating operator. 1

In case the originating'operator desires to rering the subscriber she connects battery to the tip ofthe toll line by means of a ringing key in the cord circuit which causes 1400/20 cycles to be applied to the line. This is received at the inward end and causes relays to function to transmit a 1000/30 cycle answer-back signal to the originating end. This answer-back signal cuts oil the 1400/20 cycle signal. I

Receipt of the 1400/20 cycle signal and its subsequent disconnection transmits an order tone to the originating operator and reconnectsthe inwardoperators telephone in the usualmanner in addition to flashing the connect or guard lamp. If the subscriber is to be rerung the inward operator actuates a position rering key 712 which causes the subscribers bell to be rung, the same as on the original call, and the operators telephone set to be disconnected.

7 When the originating operators cord supervisory lamp lights. if the called subscriber is not to be rerung, the operator withdraws her plug from the line whereupon 1400/30 cycles is transmitted to the distant end which causes the disconnect lamp at the inward position to be lighted and :1 1000/30 cycle answer-back signal to be transmitted to the originating end which removes the 1400/20 cycle disconnect signal which in'turn causes the 1000/30 answer-back signal to be disconnected.

The circuit now restores to normal when the inward, operator disconnects from the trunk.

' Detailed description A more detailed description of the circuit operation Wlll now be given.

out jack 101 of the toll line L extending to adistant tolloflice, relay 102 operates in a circuit including its left hand winding and the nature of a hybrid transformer.

contacts of relays 109 and 117, which in turn operates relay 103 in a circuit from ground at contact of relay 119. This relay operates relays 104, 105 and 301, this latter relay changing the normal tuning of the voice frequency receiving circuit, Fig. 3, from 1400 cycles per second to 1000 cycles per second. The circuit for operating relay 104 can be traced from battery, winding of 104, upper and lower contacts of relay 110 to ground atthe lower contacts of relay 103.

Relay 105 operated, energizes busy signals, such as 106, at all outward appearances of the line at the originating end and opens the line termination, comprising resistance 107 and capacity 108, normally in bridge of the line. 1 Y

Relay 104,.operated, locks at its lowermost contacts, under control of relays 108 and 109 and operates relays 110 and 111. Relay 110 locks up under control of relay 103. lVith relays 111 and 104 operated voice frequency current of 1400 cps, interrupted at a 20 cycle rate, from the source 112, is connected to and i sent out over the toll line L until a 1000 cycle answer-back signal, interrupted at a 30 cycle rate, is received over the'line from the distant end.

Inter-posed in the line L is a directional selection circuit arrangement 113 which is of Such a directional circuit arrangement is disclosed and claimed in the patent to Geoge Crisson 1,755,243, issued April 22, 1930 and, as it forms no part of the present invention, it is deemed suflicient to state that this arrangement is so constructed and arranged as to prevent any portion of the voice frequency current applied to the line L, by the relay 11.1, from flowing over leads 114 and 115 into the signal receiving circuit Fig. 3 while at the same time diverting voice frequency signals received over the line from the other end and transmitting them, without attenuation, to the signal receiving circuit. It will, therefore, be understood that the 1400/20 cycle signal, transmitted over the line as a calling or connect signal is not impressed on the signal receiving circuit but that the 1000/30 cycle answer-back signal transmitted from the distant end is shunted into the receiving circuit to cause operation of the polarized relays 302 and 303.

When the 1400/20 cycle connect signal was transmitted over the line it arrived at the distant end and entered the signal receiving circuit Fig. ,4, through the directional selection circuit 513 and leads 514 and 515 without attenuation. This signal wasdetected and. amplified by the vacuum tube detector 410 and amplifier 411 and caused. relay 402 to vibrate its armature between its back and front contacts which operated relay 408 which in turn operated relay 409. This relay operated circuit (Fig. 3)

slows relay 412 which operated relay- 516-.

Belay .516 operated relays 517, 518 :and'5'05. J Relay 4112 is maderslowto operate inordei' to difierentiate between false signals such as static disturbances, "and the sustainedrca'll Relay 518 operated relay 511 and applied an answer-back signal of 1000/30 cycles from source 523, to the line. Relay517 lockedup under controzlof relays 503 and 519 and transferred the linefroin jack 501 to the inward position at contacts of relay 715; Relay 505 operated the busysi nals, as for example 506, at each operators position at which the line appeared. it also removed the .line termina tion, consisting of resistance 507 and capacity 5'08,normally in bridge :ot the line. Relay 517 operated opens the operating circuit of sleeve rel ay 502 which prevents transmission of a .call signal in the opposite direction in case an operatorsliould plug into jack" 501. Vlhen the 1000/30 cycle answer-back signal was received atthe outgoing or originating end of the line it entered the signal receiving thru the directional selection circuit 113' and the leadsllt and 115 without attenuation. This signal was detected by detector 310 and amplified by ampli fier 311 and caused relay 303lto ibrate its armature to cause thesequentialoperation of relays 305 and 306 'whicliilattcr relay operated relay 108'. This released relay by opening its-locliing path. Belease'of relay 10 1 opened the circuit ofrclay 111 which released and disconnected the 1400/20 cycle calling or connect signal originally applied to the line; Discontinuance of 'this calling or connect signahre leased relays 402, 408., 4509, 112, 51 6 and 518 which in turn released relay 511 and disconnectedthe 1000/30 cycle answer-hack signal. Discontinuance of this answer-back signal released relays 303, 305, 306 and 1'08 in turn. 1 Returning now to the inward or-called end of the line; when'vrelay 517 operated it com pleted an energizing circuit for relay 702 which in turn closed energizing circuits to 0p erate relays 703-and i and connected (batteryto steadilylight the connect'ilamp "705. c Belay 70-connected the'tone source 706 to the line; over contacts of relay517', while the circuit is waiting to beconnected' tothe operator. When relay 703 operatedit closed a circuitto energize relay 707 whichin turn completed all-energizing circuit to operate relays 7.0.8 and? 09 infseries Relay 708. closed a. circuit to operate relay 710, under control of interrupter 11, and with relay 709 oper- I ated, the" lamp 705 was transferred from steady battery to an iuterruptedeource of potential at the contacts ofrelayj710ithereby causing the, lamp 705150 flash as :aniindication to the inward operator thather telephone set was connected to this particularrline.

709 .operatiiigzopened the energize ingcircuit of relay704c'tliereby disconnectihig thetone source 706 from the line. i Relay 712 also operated which, however, performed no useful function at this time. Further, relay 709 connected-the operators telephone circuit (Fig. :6) to the line and connected battery overcontacts of relays 702 and 715 to conductor 713 to sequentiailyfloperate. relays 6 1,602, 603, 604, 605,606 and 607 Operation of relays 601130 605 in sequence caused 3 three short impulses or spurts-of tone to be applied to the line as the well known order signal which indicates to the distant 0r origmating operator that the operator at the called exchange is connected to the line and" ready to receive the call. Relay 607 released relays 5601 to 606 and locked itself up to :bat-

tery on conductor 713. Operation of relay 607 also short-circuited condensers 7608 and 609 and removed the secondary of the tone" transformer 610 from its normal bridge rela tion with the line. The inward operator (Fig. 6) is now 111 conversational connection with the-outward toll operatorconnected to theliiie at jack 101. Y s Toll line connected to switching Mean/7c Letit'now be assumed that asubscriber S (Fig.8) was desired and therefore the in- Ward toll operator inserted the'inward plug 7 010i the toll line into the trunkjaclr 801 leading to a B' operators position havingiaccess to the lineof the desired subscriber.

When plug 701 was inserted in jack-801 relay 714 operated which in turn operated relays 715 and 716. Relay 718 is margina ltand does not operate at this time. Relay 71'5 opens the operating circuit for relay 703 of the sequence circuit which released relays 707, 708 and 709 in turn. Relay 7 08 perma-c nently releases relay 710 and stopsthe flash ing of lamp 705, Relay -7'15 also opens the steady battery supply for lamp 705 and also disconnects the battery from the lead 713 1 thereby releasing relay 607 in the inward toll operators circuit :(Fig; and restores that circuit to normal in readiness for another call. Release ofre'lay 709 disconnects the operators circuit (Fig. 6) from the line. Relay 715 also connects the line through to the trunk.

When the plug was inserted in the trunk jack 801, relay 802 operated which operated relay 803 and finally caused operation of 're-' lay804 to connect the B operatofis telephone set tothe trunk andsend back the usual two zips or impulses of order tone;

Relay 71 6611 opera-ting connected battery throughcoil 717to the tip of, the trunk which caused relay 805' in the trunkto operate which operated marginal relay 806, by short C1IC1'1lt1ng-tl10 upper, "high resistance, :winding of relay 811,,which in turn operated ringing relay 807 to applyringingcurrent to the trunk conductors in readiness to ring the sub scriber when the plug 808 is inserted in the subscribe'rs jack.

Tmmlc connected to called subscriber? line winding. This caused the marginal relay 718 in the toll line .to' operate which operated relay 719. Relay 719 operated relay 511 which connected 1000/ cycles, from source 520,.to the line which was received at the originating end by the receiving circuit (Fig. 3) and caused relays 302, 308 and 309 to operate thereby operating relay 121 which shunted the left hand high resistance winding of relay 102 with its right hand low resistance winding thereby decreasing the sleeve resistance of the associated toll cord and lighting the cord supervisory lamp in the well known manner. 'This1000/20 signal persists, thereby maintaining the toll operator supervisory lamp lighted, until the called subscriber (Fig. 8) answers.

Operation of relay 719 operates relay 723, over the lower contacts of relay 716, and provides a holding path for relay 716 which otherwise would release when relay 723 operated. Relay 723 locks up under control of relay 714. I

:Relay 719 also closes a circuit from slowoperating interrupter 726 to relay 724 thereby causing that relay to alternately open and close'its contacts in step with the interrupter and alternately disconnect and connect the battery supplied to the tip of the line. This alternately releases and operates relays 805, 806 and807 in sequence to ring the subscriber bell at the usual machine ringing rate of two seconds ring and 4 seconds silent.

C'allcd subscm'ber answers When the called subscriber answers supervisory relay 812 in the trunk circuit operated thereby short-circuiting relay 810 and cansing it to release which again reversed the battery flowing through polarized relay 811. This directional change of current flow re leased relay 811 which again increased the resistance of the sleeve circuit, by removing the lowresistance shunt from the upper and high resistance winding of relay 802. This change to a high resistance caused marginal relay 718 to release and in turn release relays 719 and 511 which latter relay in releasing removed the 1000/20 cycle signal and reconnected the toll line through to the trunk, Relay 716 was also released by relay 719 which in turn released relay 805 in the trunk. Release of this relay (805) removed the short circuit around the up er, high resistance, winding of relay 811 which released marginal relay 806 which in turn released the ringing relay 807 and disconnected ringing current from the called sub scribers line.

Removal of the 1000/20 cycle signal permitted relays 302, 308 and 309 in the receiving circuit, Fig. 3, at the outgoing end of the toll line to release thereby releasing. relay 121 which removed the low resistance shunt from the left hand winding of relay 102 by opening the path to ground through the right hand winding thereby increasing the sleeve circuit resistance of the toll cord to extinguish the outward operators supervisory lamp as asignal that the called subscriber had answered. The toll line is now connected through to the called subscriber and ready for conversation.

Called subscriber flashes or disconnects Each time the subscriber S restores his switchhook relay v812 releases which permits relay 810 to again operate thereby operating polarized relay 811 which changes the trunk-sleeve resistance from high to low thereby operating relay 718 in the toll line circuit. Relay 718 operates relay 719 which in turn operates relay 511 which connects 1000/20 cycles to the line. This signal is received at the originating end and 0p erates relays 302, 308, 309 and 121 which changes the outward toll jack sleeve resistance from high to low and causes the outward toll operators supervisory lamp to light. If the called subscriber hangs up his receiver the supervisory lamp at the outward toll position will burn steadily, but if he moves the switchhook up and down the supervisory lamp will flash.

.Origjz'mting operator rem'ngs In case the originating operator desires to rering the subscriber S (Fig. 8) after he has replaced his receiver on the hook, operation of the toll cord ringing key will connect battery to the'tip of the line operating relay 122 which in turnoperates relay 104, which operates relay 111. Relay 104 looks up under control of relays 109 and 108. Relays 111 and 104 operated connect 1400/20 cycle current from source 112, to the line which persists until an answer-back signal is received from the distant end.

When the 1400/20 cycle signal is received at the distant toll ofli 3e relays 402, 408, 409, 412 and 516 operate. Relay 516 operates relay 518 and opens the energizing circuit for relay 702. Relay 518 operates relay 511 which relay combination connects the signaling source 523 to the line which transmits ii-$860346 I a a v: 100Q/30-1'cyc1e a answer b ack signal :to I the i 2305," 306 -and-2-1 08.-}: Relay 108freleases relay v -ii04f=byzopeningiits path. re'layilll' thereby-disconnecting the'i1400/20 cycle 2 signal it which permits relays 402, I 408,

409, 412 and 516'at the distant end to release. idtelayi516 releases relay 5'18 which intu'rn redeases relay 511 thereby disconnecting I the 1000/30 cycle 1 answei back signal which re leasesrelays 303, 305, 306 and- 1108 at the ori ginating end. Q I r a 1 1 Whenrelay 7.02releas'ed it operated relay 725-- which looked undercontrol Tot relays 723 and 714. 'j Operation: of relay 7 25: released relays 'tl5 and 719. The release of. relay 715 wdisc'onnecte'd the, toll line 'fromthejack. 1

Whenwelay 516 released, 1 due to'the :dis

connection of the 1400/-signal, relay' 702 :reoperatedwhich again completes an energizing circuit for relay' 704 which connects atone to the line. relay' 703 fof the sequence circuit which opcrates -relays'707, 708'and 709 which causes releases relay 704 and disconnects the tone from theline. When relay 709'operated it also connected the operators telephone cir cuit to thetoll line and caused the operation i V leased which in turn releasedzr'elayfr' 21. ;'*-inward"iendfofthe toll line is new in nornial of relays 601 to 607 to, again transmit three zips of order tone in the manner previously described. When the inward opera- 'tor is brought in, as indicated bythe lamp 705 flashing, originating operator. If the called subscriber is to be rerung the inward operator operates position rering'key 611 which deenergizes relay 723, due to its diiferen'tial con- 7 y V H station, a recennng statlon,

nection, which in turn releases relay 725 and reoperates relay 716.

From this point the circuit functions the same as previously described when the op- Originating operator disconnects cycles to the distant toll office whereit operi ates relays 403, 405, 406," Relay 519 releases relays 4.07, 508 and 519. 517 and 505 which latter relay opens the busy signal circuit and permits busy signal 506 to restore. Relay operates relay 511whioh connects signal source 523 "to. the line which transmits a 1000/30 cycle answer-back signal to the A i :of alternating current: of difie'rent :character- I 3181310 eat? therreceivingstation; zmeans iresponoriginating end to operate relays 303, 305, 306, 307,108, and 119i. Operation of relay 108 releases relay 103'which in turnreleases Relay 104Telea-ses I which restores the' tuning of' the-receiving Relay 7 O2 'alsooperates.

relay. 7 20 fromi-batteryoni the tip conductor the'connect lamp- 705 to flash under control of interrupter 711 and relay710. Relay 7 09v she acts as instructed by the erator first plugged into the switching trunk.

519' also operates relay 518 Which-in turn; D

i applre d to said 2 11116, 5 s1 gnalr receiving i means at the receiving station adaptedito'zbe 'com rrelays 110 1and 1O5; this latter relay opening soriginatlng ioflice wh1chaop'erates' relays 303, I the" busy signal 'circu-itandpermitting busy signal 106 to r'estorei The -release :of 'relay 103 also releases. the change tuning relay 301 circuit to 1400' cycles ing readiness to receive incoming calls or connect signalsotthat'fre- .gquency transmitted from the distantend. Relay 110 released, releases relay 109 "which inturn releases relay '111 -which removes' the 1400/30 Cycle signallfrom the line which releases relays 403,405, 406, 407, 508ian'd 519. ltelay 519 released; releases relay 518 which I -,in turn" releases relay 511 "and removes the '1 1000/30' cycle .answer backi signal.

ee *When' the 1000/30 cyc1e answer-back signal ceases relays 303, 3055, 306,- i307 108 and 119 release-and. the :circuit -ati the outward? end of the? toll; line is in 'xitsnormal condition.

; tantiend of ithe line operated it also operated: relay-.720 which iirturnoperated relay 7 21. J Relay- 721 closed. a holding .1 path ifor of the trunk. :Relay 72lf-alsolightedYthe disconnect :lamp: 722. and opened-the sleeve Iconductor thereby releasing relaysl714, 802iand 803. i i I I Whenithe a inward "toll "operator removed the plug 7.0];"f-rom as .j ac]: I801 relay '720: re-

.The

condition. -i .Qperationaf of the circuit :inithe 1 opposite "direction ris identically the same. as the: operm ationjust described and consequently will notibe-repeated; a

' .isiclaimed is z 1.1111,. a signaling system, a 'transmittin'g j a 'lineiinterconnectingsaid stations; a source oif alternating signal current of predetermined:characteristic at said transmitting station adapted to be appliedtto; said line; signal TQCBlVTlDgZiII IGaDS at the receiving station: adapted" to be Z'COII- 310 trolled hy'saidsignal current, ;a second'source ol? alternating current of difierent characteristic ah the receiving "station; means "responsive to' thBwCODtIO'l' OI said: signal irecciving v Ineans to ap'plysaid second source'of current' 115 to the line;-i and; means atcthe transmitting V stationrre'sp onsi've =solely:tot*said second current' to@disconnectsaid first; current from the line. s e

- 2.11am signaling-system, a transmitting-120 station, a receivinga'station, *a' 'line' interconnecting said stations, "a source 20f1 alternating signal: current of predeter-mined characteristic said transmittingstation"adaptedsto'rbe trolled by said signal current, a second source sive'ito ,-.-the control ofi said signal-receiving 113 0 means to apply said second source of current to the line, means at the transmitting station responsive to said second current to disconnect said first current, and means at the receiving station responsive to disconnection of said first current to disconnect said second current from the line.

3. In a signaling system, a transmitting station, a receiving station, a line interconnecting said stations, a source of alternating signal current of predetermined characteristic at said transmitting station adapted to be applied to said line, signal receiving means at the receiving station adapted to be controlled by said signal current, a signal device at said receiving station controlled by said receiving means, a second source of alternating current of different characteristic at the receiving station, means responsive to the control of said signal receiving means to apply said second source of current to the line and to actuate said signal device, means at the transmitting station responsive to said second current to disconnect said first current and means at the receiving station responsive to disconnection of said first current to dis-. connect said second current.

4. In a signaling system, a line, two stations interconnected thereby, means at each station for transmitting alternating signal current of a predetermined frequency to the line, means at each station for receiving said line signal currents transmitted from the other station and for registering a signal, means, actuated when an originating signal is received at a station, to transmit back over the line cutoff signal current of a frequency different from the frequency received and means at the transmitting station responsive solely to said cutofi the transmission of the current which caused registration of the signal.

5. In a signaling system, a line, a calling station and a called station interconnected by said line, a source of alternating current associated with each station for signaling over said line, means at each station for connecting its associated signal source to the line, means at each station for receiving and translating signal current transmitted over said line from the other station, means at the called station responsive to the receipt and translation of signal current from the calling station to connect the signal source at that station to the line to transmit an answer signal to the calling station and means at the calling station responsive solely to the reception of said answer signal to disconnect said current source thereat from the line.

6. In a signaling system, a line, calling and called terminals, a call signal device and an minal of said line, means for transmitting an alternating currentsignal over said line from the callingend thereof, means responsive to current to discontinue nal current at each station, means at each sta tion for connecting its associatedsource of current to the line, means at each station for receiving and translating signal current transmitted over the line from the other station, and means automatically responsive to the reception and translation of signal current at one station to connect its associated signal source to the line to transmit an answer-back signal.

In testimonywhereof, we have signed our names to this specification this 9th day of October, 1930.

RAND S. BAILEY. NEAL D. NEWBY. DWIGHT L. MOODY.

operators telephone circuit at the called ter 

